Blocks Of Different Sizes Research Articles

Atom diffusion in a simple cubic lattice: Real-space renormalization group and Monte Carlo calculations

A three-dimensional simple cubic lattice gas is investigated by using the real-space renormalization group (RSRG) approach with blocks of different size and symmetries. We have calculated absorption isotherms and density dependencies of the pair correlation function, isothermal susceptibility, chemical and jump diffusion coefficients for different temperatures. All these quantities have also been obtained by Monte Carlo (MC) simulations. We have also obtained the density dependencies for the tracer diffusion coefficient by MC simulations. Despite the fact that both methods constitute very different approaches, the correspondence of numerical data and theoretical results is rather good. We conclude that the RSRG method can be applied to the three-dimensional lattice gas system discussed here to characterize its thermodynamic and kinetic properties.

Not so good vibrations

Pliny the Elder was one of the first to record it 2,000 years ago: termites are noisy eaters. Their loud chewing generates acoustic emissions that have been proposed to be a method of detecting cryptic attack. But a team from the Commonwealth Scientific and Industrial Research Organisation and the University of New South Wales in Canberra, Australia, wondered whether worker termites might be able to detect vibration/acoustic signals generated by their foraging and use these signals to determine the size of the piece of timber they are attacking.TermitTermites have a reputation of being voracious and non-discriminating feeders, consuming all wood that they can find. The 2 million homeowners in the US and many elsewhere who require termite treatment each year know the problem. But Theodore Evans and colleagues, reporting in the Proceedings of the National Academy of Sciences (published online), believe this reputation is not deserved. In fact, termites can be highly selective feeders. Wood species palatability and hardness are important, as are the defensive chemicals made by the plant. But these appear not to be the only criteria by which termites assess a potential food source, as anecdotal accounts abound of termites not consuming a piece of palatable wood after finding it.Termites cause enormous damage, as shown in this house in New Orleans in the southern US, but new evidence suggests that for at least one species the size of potential timber food is of key importance in determining whether or not they decide to feed on it. (Photograph: Oxford Scientific Films.)View Large Image | View Hi-Res Image | Download PowerPoint SlideOne possible issue is the potential quantity of food. Different termite species that live in the same habitat feed on particular sizes of wood, some species targeting smaller fallen twigs and sticks and others targeting larger fallen branches or entire trees. Such variation in choice may have evolved to avoid competition, but how does a termite assess the size of a piece of wood? Termites come into contact with only a tiny piece of any wooden object and decide to eat it based on this minor contact. The decision to eat a piece of wood is made by the termites before the piece of wood is measured physically. They do not assess the linear dimensions, which would expose them to predators, or evaluate it visually as worker termites are blind.The possibility that termites could use vibroacoustic signals to assess wood size has been suggested previously following observations that Cryptotermes termites quickly responded to the volume of food given, without having the possibility of measuring the food physically.The team therefore decided to test whether termites of the Cryptotermes domesticus species might be able to discriminate between different sizes of wood. The team constructed experiments that presented termites with blocks of wood with a standard cross-sectional diameter of 20x20mm but of either 20mm or 160mm length. The insects were placed in a gap between the two faces of the timber blocks so that they were not able physically to assess the length of each block.The team found that the termites, when presented with a choice, preferred the shorter 20mm block. To test whether the termites might be using vibration signal to assess the blocks, the researchers carried out two experiments. They recorded the vibration signals produced by termites placed in a hole in blocks of wood of lengths varying from 20 to 160mm long. They then examined the influence of some of the recorded signals on termites faced with wood blocks of different sizes along with the influence of two artificially synthesized signals.The team found that when they played the vibration signals recorded from the larger block into the smaller block, the termites’ preference for the smaller block disappeared, but when the signal from the smaller block was played the preference was maintained. The termites did not change their behaviour in response to artificial noise signals.The researchers believe the demonstrated preference for smaller pieces of wood may be a mechanism to avoid competition with larger species of termite attracted to larger pieces of wood.But while individual termite species might be fussy, the news is not good for those whose home timbers have been deemed an ideal feast by whatever species finds this source and size of wood attractive.

Termites assess wood size by using vibration signals

Contrary to the common perception that termites are indiscriminant eaters, termites choose their food carefully; however, the methods by which they choose food are not well understood. Using choice experiments and recordings of termites feeding on wooden blocks of different sizes, we show that worker drywood termites (Cryptotermes domesticus) use the resonant frequency of a block of wood to assess its size. Drywood termites showed differences in their response to vibration recordings of termites compared with artificially generated signals, suggesting that they can discriminate the source of vibration. Furthermore, fewer workers matured into neotenic reproductives when recorded termite signals were played, suggesting that vibration signals play an important role in termite communication.

Low-complexity progressive image transmission scheme based on quadtree segmentation

A novel progressive image transmission scheme based on the quadtree segmentation technique is introduced in this paper. A 3-level quadtree is used in the quadtree segmentation technique to partition the original image into blocks of different sizes. Image blocks of different sizes are encoded by their block mean values. The relatively addressing technique is employed to cut down the storage cost of block mean values. In the proposed scheme, the number of image hierarchies can be adaptively selected according to the specific applications. By exploiting inter-pixel correlation and differently sized blocks for segmentation, the proposed scheme provides good image qualities at low bit rates and consumes very little computational cost in both image encoding and decoding procedures. It is quite suitable for real-time progressive image transmission.

A random multifractal tilling

We develop a multifractal random tilling that fills the square. The multifractal is formed by an arrangement of rectangular blocks of different sizes, areas and number of neighbors. The overall feature of the tilling is an heterogeneous and anisotropic random self-affine object. The multifractal is constructed by an algorithm that makes successive sections of the square. At each n-step there is a random choice of a parameter ρi related to the section ratio. For the case of random choice between ρ1 and ρ2 we find analytically the full spectrum of fractal dimensions.

A random multifractal tilling

We develop a multifractal random tilling that fills the square. The multifractal is formed by an arrangement of rectangular blocks of different sizes, areas and number of neighbors. The overall feature of the tilling is an heterogeneous and anisotropic random self-affine object. The multifractal is constructed by an algorithm that makes successive sections of the square. At each $n$-step there is a random choice of a parameter $\rho_i$ related to the section ratio. For the case of random choice between $\rho_1$ and $\rho_2$ we find analytically the full spectrum of fractal dimensions.

Diffusion of particles adsorbed on a triangular lattice: pairwise and three-particle interactions

In the present paper, the influence of both pairwise and three-particle interactions on the mobility of adsorbed particles diffusing on a lattice with triangular symmetry has been studied. Two different techniques has been used for describing the surface diffusion phenomenon. On one hand, explicit expressions for the chemical and jump diffusion coefficients have been calculated by using real-space renormalization group (RSRG) approach. A number of the RSRG transformations with blocks of different sizes and symmetries have been investigated. In particular, it has been shown that the precision of the method depends strongly not only on the number of sites in the RSRG blocks but also on their composition and structure. On the other hand, numerical simulations by using the Monte Carlo scheme has been used to simulate the process of particle migration. Using both methods, adsorption isotherms for different temperatures and the coverage dependencies for the thermodynamic factor and the chemical diffusion coefficient have been calculated. The behavior of the above mentioned quantities has been compared when the adparticles interact via only either pairwise or three-particle interactions. Despite the fact that both methods constitute very different approaches, the correspondence of numerical data with analytical results is surprisingly good. Therefore, it can be concluded that the RSRG method can be successfully applied for lattice gas systems to characterize the thermodynamic and kinetic properties of strongly interacting adsorbates.

A multiscale analysis of fixed-end simple shear using molecular dynamics, crystal plasticity, and a macroscopic internal state variable theory

We examine FCC nickel undergoing simple shear by using three different numerical frameworks formulated at three different size scales. The three frameworks included embedded atom method potentials used in molecular dynamics simulations, crystal plasticity used in finite element simulations, and a macroscale internal state variable formulation used in finite element simulations. Simple shear simulations were performed in which the specimen aspect ratio was varied to give insight into the homogeneous and inhomogeneous aspects of large deformation. This study revealed that the `apparent' yield stress was sensitive to the specimen aspect ratio except when the length-to-height ratio reached about 8 : 1, the yield stress remained constant. The three numerical frameworks gave similar qualitative responses related to inhomogeneous stress and strain distributions in the corner regions of the specimens and also similar responses in the centralized homogeneous deformation region. However, when comparing the shear stress distribution for the finite element analyses to the atomistic simulations, a much narrower distribution arose for the finite element analyses due to the lack of thermal vibrations experienced in the atomistic simulations at 300 K. A 10 K an atomistic simulation which dampened out the high frequency thermal vibrations verified this reasoning. Three different sizes of blocks of atoms were also used in the atomistic simulations and the results showed very similar stress and strain distributions with respect to each other indicating that no size scale effect is evidenced when normalized by the global shear stress. However, a size scale effect exists related to the global (volume average) shear stress in the specimen. As the specimen size increased, the yield stress decreased. Finally, when comparing the three different numerical frameworks, the location of maximum dislocation nucleation occurred at the location of the maximum plastic spin, stress gradients, and strain gradients.

Non-linear micropolar and classical continua for anisotropic discontinuous materials

Non-linear Cosserat and Cauchy anisotropic continua equivalent to masonry-like materials, like brick/block masonry, jointed rocks, granular materials or matrix/particle composites, are presented.An integral procedure of equivalence in terms of mechanical power has been adopted to identify the effective elastic moduli of the two continuous models starting from a Lagrangian system of interacting rigid elements. Non-linear constitutive functions for the interactions in the Lagrangian system are defined in order to take into account both the low capability to carry tension and the friction at the interfaces between elements. The non-linear problem is solved through a finite element procedure based on the iterative adjustment of the continuum constitutive tensor due to the occurrence of some limit situation involving the contact actions of the discrete model.Differences between the classical and the micropolar model are investigated with the aid of numerical analyses carried out on masonry walls made of blocks of different size. The capability of the micropolar continuum to discern, unlike the classical continuum, the behaviour of systems made of elements of different size is pointed out. It is also shown that for anisotropic materials, even in the elastic case, the micropolar solution in general does not tend to the classical solution when the size of the elements vanishes.

The Effect of Reservoirs on the Rock Foundation of High Dams

Any man-made water storage (reservoir) produces additional loading in a local area of the Earth’s crust, which does not leave unaffected the local hydrogeological conditions. These factors exert an influence on the properties and the state of the enclosing rock massif; still, in designing and performance analysis of large dams, they are commonly left out of consideration. The available experimental data provide evidence that, under definite engineering geology conditions and operational regimes, these factors may cause serious destructive changes in the basement of engineering structures and complicate their performance efficiency. In this paper, we analyze the hazard associated with such destructive changes based on follow-up regime observations of the abutment in the Inguri arch dam and arch-gravity dam of the Sayano-Shushenskaya hydroelectric power plant (HPP) under different operational regimes of their reservoirs. Inguri arch dam. The foundation and abutment of the dam and also part of the reservoir bed at the dam are composed of Low Cretaceous limestones, dolomitic limestones, and dolomites, with their beds extending jointly to the afterbay. The rock massif features an alternation of beds of different thickness — from thin to very large. The primary bedding is complicated by the superposition of tectonic joints. At the foundation of the massif, six systems of joints are distinguished, of which the most developed are bedding joints, steeply dipping (subvertical) joints parallel to the slope, and flat joints subnormal to the slope [1]. The lefthand abutment is complicated by a tectonic dislocation of the fault-shift type, which is a feathering-out of the local Ingurishskii fault. In terms of tectonic jointing and surface weathering, the massif is divided into a number of engineering geology elements that differ substantially in physicomechanical and seepage properties [1]. Special regime observations were conducted to monitor the behavior of rock masses at the foundation and abutments of the dam. Along with the standard observations (KIA System), other geophysical measurements (seismic, ultrasonic, electric, thermometric) were carried out; deformation properties of rocks were remeasured using unique hydraulic cushions located at different distances from the day surface [3]. Most of the observations had begun before the Inguri reservoir started filling in 1978 (the filling continued for about 15 years). The measured geophysical parameters — velocities of seismic (V s ) and ultrasonic (V us ) elastic waves 2 and electrical resistance n — were used to to follow changes in the properties of rocks in the foundation and abutments of the dam during the filling of the Inguri reservoir and its various service regimes [2, 4 – 6]. The main results may be summarized as follows. Under the filling and service conditions, sharp spatio-temporal changes in parameters V s , V us , and n were observed that exceeded the measurement error by 1 – 1.5 orders of magnitude. The changes in V s , V us , and n differed substantially in subsurface and deep-seated areas of the rock massif, as well as in structural blocks of different size. In terms of the time trend, the rock massif under study can be divided into three zones: — high-trend zone — a near-surface portion of the massif, 80 – 90 m in depth extent where the largest fluctuations in V s and n were recorded; — moderate-trend zone — a portion of the rock massif moderately responsive to effects exerted by the reservoir; this zone is demarcated between 80 – 90 and 200 – 250 m; — zero-trend zone, practically insensitive to the reservoir effects, where the recorded values of V s and n are fairly constant; the depth of occurrence of this zone (measured nor

Collective surface diffusion of repulsively interacting particles on a triangular lattice: Comparison of real-space renormalization group and Monte Carlo approaches

A two-dimensional lattice-gas model with triangular symmetry is investigated by using the real-space renormalization group (RSRG) approach with blocks of different size and symmetries. It has been shown that the precision of this method depends strongly not only on the number of sites in the block but also on its symmetry. In general, the accuracy of the method increases with the number of sites in the block. Using the RSRG method, we have explored phase diagrams of a two-dimensional Ising spin model and of a triangular lattice gas with pair lateral repulsive interactions. We have calculated: (i) adsorption isotherms and thermodynamic factors for different temperatures and (ii) the coverage dependence for the pair, three, and four nearest-neighboring particles correlation functions, the tracer, jump, and chemical diffusion coefficients using four different models of adparticle jumps. All these quantities have also been obtained by Monte Carlo (MC) simulations. Despite the fact that both methods, RSRG and MC, constitute very different approaches, the correspondence of the numerical data is surprisingly good. Therefore we conclude that the RSRG method can be applied, at least for the systems discussed here, to characterize the thermodynamic and kinetic properties of strongly interacting adsorbates. It is also shown that drastic changes in the surface diffusion coefficients occur when (i) lateral interactions force ordering of the adatoms via second-order phase transition and (ii) different models of adparticle jumps are used.

Twinning and defects in N-Nb2O5.

N-Nb(2)O(5) [C2/m (No. 12), a = 28.51, b = 3.830 and c = 17.48 A, and beta = 124.8 degrees ] has been investigated by means of selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). N-Nb(2)O(5) is domain twinned, with the twin plane perpendicular to the c* axis. The domains are rather small and the domain twinning can sometimes be best explained as stacking faults. A second type of coherent twinning at an angle of 90 degrees to the other two domain directions was also found. These domains are linked together by areas containing blocks of different sizes, similar to the disordered block arrangement observed in M-Nb(2)O(5).

An analytical procedure for estimating residual stresses in blocks containing crossbores

Intersecting bore geometries are used in a number of industrial applications such as the fluid ends of reciprocating pumps and have regions with high stress concentration. To increase the fatigue life of a fluid end, a reduction in the operating mean stress is helpful. This can be achieved with the introduction of compressive residual stresses in these critical regions by means of proof loading or autofrettage. Accurate estimation of fluid end fatigue lives necessitates accurate evaluation of the residual stresses induced by autofrettage. In this paper, finite element models were used to obtain hoop stress to pressure ratios, at the most highly stressed plane, in blocks of different sizes and bore ratios. The hoop stress to pressure ratios were used along with Neuber's rule and kinematic hardening to select an autofrettage pressure and to estimate the elastoplastic residual stresses on this plane. The suggested method estimates residual stress magnitudes close to finite element solutions, and eliminates the need for a lengthy and costly elastoplastic finite element analysis.

Adatom diffusion on a square lattice. Theoretical and numerical studies

A two-dimensional lattice-gas model with square symmetry is investigated by using the real-space renormalization group (RSRG) approach with blocks of different size and symmetries. It has been shown that the precision of the method depends strongly not only on the number of sites in the block but also on its symmetry. In general, the accuracy of the method increases with the number of sites in the block. The minimal relative error in determining the critical values of the interaction parameters is equal to \(\). Using the RSRG method, we have explored phase diagrams of both a two-dimensional Ising spin model and of a square lattice gas with lateral interactions between adparticles. We also have investigated the influence of the attractive and repulsive interactions on both the thermodynamic properties of the lattice gas and the diffusion of adsorbed particles over surface. We have calculated adsorption isotherms and coverage dependences of the pair correlation function, isothermal susceptibility and the chemical diffusion coefficient. In addition, we have included in our analysis the interaction of the activated particle in the saddle point with its nearest neighbors. We have also used Monte Carlo (MC) technique to calculate these dependences. Despite the fact that both methods constitute very different approaches, the correspondence of the numerical data is surprisingly good. Therefore, we conclude that the RSRG approach can be applied to characterize the thermodynamic and kinetic properties of systems of particles with strong lateral interactions.

Caracteres structuraux et dynamiques d'un bassin en transtension; la plate-forme tunisienne a l'Ypresien terminal

Abstract In Tunisia, Ypresian carbonate deposits occur on a platform preserving vestige of an inherited fault network. The fault network delineates blocks of different sizes accounting for the platform morphology and in turn for variation in thickness of the Ypresian sequence. The nummulitic limestone carapace of the Ypresian sequence is fractured by faults and joints of various orientations which are systematically sealed by marly beds of early Lutetian age. This indicates that the fault network was reactivated during late Ypresian. Geometric and kinematic study indicates that this strike slip late reactivation is accomodated by normal fault. These structures originated in soft sediment undergoing diagenesis. Depending on bed competency, both ductile and brittle deformation features were recognized in the fault. This superficial tectonic event represents, a recent reactivation of ancient fractures cartographically located on the boundaries of late Ypresian megablocks. Kinematic study of the deformation within and along the boundaries of one of these blocks, (Ousseltia block), indicates a late Ypresian, early Lutetian strike-slip distensive faulting dynamic. Stress-field orientation indicates a rapid re-orientation in time from a predominantly NW-SE extensional tectonic to a NE-SW extensional event. Stratigraphic dating of that tectonical crisis coincides with a turbulent period of relative motions between Europe and Africa.

A DCT-based spatially adaptive post-processing technique to reduce the blocking artifacts in transform coded images

We propose a discrete cosine transform (DCT)-based post-processing technique to alleviate the blocking artifacts in transform coded images. In our approach, the high-frequency components, mainly caused by the edge components, are examined through two steps. First, two adjacent homogeneous blocks from the block boundary are found, where the homogeneous block is defined as the block in which no adjacent pixels' difference is larger than the difference of the block boundary. Second, the local frequency characteristics in the homogeneous block are examined through the DCT. Then, we derive the relation between the DCT coefficients of two homogeneous blocks of different sizes. By considering the information about the original edge and the relation, we can detect the high-frequency components, mainly caused by the blocking artifact. The performance of the proposed technique is evaluated on both still and moving images. The simulation results indicate that the proposed technique reduces the blocking artifacts effectively and preserves the original edges faithfully, and its performance is very robust to the degree of degradation in the decoded images.

Vibroseismic simulation for rehabilitation of water flooded reservoirs

A correlation between oil rates and earthquakes was observed in the 1970s. It resulted in the first attempts to use the energy of seismic waves to mobilize residual oil spread in the reservoir in the form of drops of different sizes, and to rehabilitate depleted oil fields with high water production. Laboratory tests showed that oil displacement can be increased by application of low-frequency vibration. It was also confirmed by field tests (results reported at VI EOR ES, 1991): oil production due to vibroseismic stimulation increased by 30-40%. However, estimations show that such an increase in oil production does not occur with low-frequency vibration. Most probably some unknown phenomena exist which impact on the mechanism of seismic vibration-induced increases in oil production. The object of this study was the development of an analytical model of vibroseismic stimulation to explain the mechanism of residual oil mobilization. Such a model can provide the basis for effective use of vibration stimulation. The model oil-saturated formation consists of blocks of different sizes. Each large block includes several blocks of smaller sizes. Block sizes depend on the geological processes taking place during their formation, while correlation between their sizes does not depend on properties of constituent materials. Core measurements taken in the millimetre range and analysis of photographs of layer distribution in open hole taken in the metric range show that correlation between the large and small blocks occurs over a rather small range and varies between 2.91 and 3.43. Simulation of vibroseismic impact on a formation shows that a process of low-frequency energy transfer from larger blocks to smaller ones, producing high-frequency vibration, takes place. These high-frequency vibrations provide conditions under which capillary forces, retaining oil drops in the porous media, are destroyed, improving conditions for oil mobilization. These results agree with experimental data of noise measurements recorded during pilot commercial tests of vibroseismic action at different oil fields in Russia. Thus the possibility of residual oil mobilization by applying low-frequency vibroseismic stimulation was confirmed both theoretically and in laboratory and field tests. The results received were an essential part of the creation of the technology for vibroseismic stimulation of waterflooded, depleted oil reservoirs.

Adatom diffusion on a square lattice: Comparison of real-space renormalization group and Monte Carlo approaches

A two-dimensional lattice-gas model with square symmetry is investigated by using the real-space renormalization group (RSRG) approach with blocks of different size and symmetries. It has been shown that the precision of the method depends strongly not only on the number of sites in the block but also on its symmetry. In general, the accuracy of the method increases with the number of sites in the block. The most accurate results have been obtained for the largest cluster containing 34 sites. The minimal relative error in determining the critical values of interaction parameter is equal to 0.13%. It has been shown that the ``antiferromagnetic majority rule'' for the choice values of block spins gives much better results for the repulsion between the adsorbed particles, as compared to the ordinary ``majority rule.'' Using the RSRG method, we have explored phase diagrams of a two-dimensional Ising spin model and of a square lattice gas with lateral interactions between adparticles. We have calculated: (a) adsorption isotherms for different temperatures, (b) the coverage and temperature dependences of both the pair correlation function for the nearest neighboring adparticles and the chemical diffusion coefficient, (c) the temperature dependence of the specific heat, and (d) the coverage dependences of the isothermal susceptibility for different temperatures. All these quantities have also been obtained by Monte Carlo simulations. Despite the fact that both methods constitute very different approaches, the correspondence of the numerical data is surprisingly good. Therefore, we conclude that the RSRG method can be applied at least for the systems discussed here to characterize the thermodynamic and kinetic properties of interacting adsorbates.

The present-day tectonics of the Aegean as deduced from seismicity

Abstract We present a review of the seismicity and focal mechanisms for the Aegean (historical, teleseismically and microseismically computed), which we compared with the recent active faults. A very consistent trend in the T-axes within the Aegean across blocks of different size and orientation suggests that the surface tectonics of the Aegean is controlled by the deformation of the lithosphere as a whole. Some recently active faults (mostly the NW-SE-striking faults that are located west of the Aegean sea) are not associated with seismicity, some seismicity is associated with new E-W-striking faults of modest displacement that are mostly seen in continental Greece. We suggest that, due to the important amount of internal deformation of the Aegean lithosphere and the inferred rotations, the localization of the deformation changes with time and a precise timing of the recent faults activity is necessary to correlate with present-day deformation. We also suggest that, for continental crust, the work to create new fault that strike perpendicular to the main strain direction (as deduced from focal mechanisms and GPS measurements) is less than the work to reactivate faults that strike obliquely to the strain direction. We propose that a diffuse system of normal faults or grabens starts to develop, parallel to the Gulf of Corinth, and links the western termination of the North Aegean Trough to the northern end of the Kefallinia fault.

Adsorption and diffusion in a square lattice gas with strong attraction between particles: The real-space renormalization group approach

A two-dimensional lattice gas with an attractive nearest neighbor (NN) pairwise lateral interaction on a lattice of square symmetry and its equivalent two-dimensional Ising spin model have been investigated by using the real-space renormalization group (RSRG) approach with blocks of different sizes and symmetries. We have calculated (a) adsorption isotherms for different temperatures and (b) the spontaneous magnetization for the Ising spin ferromagnet. The RSRG data are compared with the well-known exact expression. The coincidence between the exact and RSRG data is rather good. It is shown that the precision of the RSRG method strongly depends not only on the number of sites in the block but also on its symmetry.In addition, we have calculated the coverage dependences of the pair correlation function for nearest neighbor adparticles, the isothermal susceptibility and the chemical adparticle diffusion coefficient at different temperatures. Furthermore, we have calculated the critical behavior of the mean square adparticle density fluctuations and of the chemical diffusion coefficient. The critical exponent is close to the value obtained by other methods. The RSRG data have been compared with results from Monte Carlo simulations. The coincidence is very good and, therefore, we conclude that the RSRG method can be applied at least for the systems discussed here to investigate the thermodynamic and kinetic properties of interacting adsorbates.